Abstract

We analyze
time series of velocities of the low‐speed stream of the solar wind plasma including Alfvénic fluctuations
measured in situ by the Helios spacecraft in the inner heliosphere. We demonstrate that the influence of noise in the data can be efficiently reduced by a moving average filter. We calculate the multifractal spectrum for the solar wind
flow directly from the cleaned experimental signal. We also show that due to nonlinear noise reduction we get with much reliability estimates of the Kolmogorov entropy and the largest Lyapunov exponent. For intermediate length scales the Lyapunov exponent and the entropy are plausibly positive locally, which exhibits sensitivity to initial conditions. This shows that the slow solar wind in the inner heliosphere is most likely a deterministic chaotic system, where noise is not dominant.